1. Field of the Invention
This invention relates in general to the construction of humidifiers for respirators and in particular to a new and useful humidifier wherein water is circulated around an evaporation surface through which inhalation air is passed from a storage tank which is maintained at a proper level by a closed container which is supported above the level of the storage tank.
2. Description of the Prior Art
In the artificial respiration of patients by means of intubation and also in the spontaneous respiration of tracheotomiced patients, the respiratory air no longer flows through the throat-nose-pharynx tract, but directly into the bronchi. Since the respiratory air does not come into contact with the throat-nose-pharynx tract, it can no longer be heated sufficiently and humidified. The result is a drying out of the respiratory tract and an impairment of the function of the ciliary epithelium. In order to prevent the respiratory tracts from drying out, it is known to provide humidifiers whose function it is to heat the inhaling air to body temperature and if possible to bring it to a value of possibly 100% relative humidity.
The known humidifers have an essential drawback that the water which evaporates therein increases the volume of the vacuum on the inhaling side. Due to the unavoidable compression at the inhaling pressure which can amount up to 120 mm of water column a critical inhaling volume difference between respiration with and without water supply in the humidifier of about 20% may occur in the respiration of infants.
The so-called cascade humidifiers are known in which the inhaling air is conducted through the heated water which is to humidify the air. Water droplets which have been carried along are retained by pellets arranged above the water surface. A disadvantage of a cascade humidifier is that the compressible volume varies with the amount of filling water. Beyond that, the apparatus is so big that it cannot be placed directly in front of the mouth of the patient. In long feed lines, the air cools off, however a part of the moisture contained in the inhaling air will thus condense. The condensate must be kept away from the patient by corresponding measures.
Humidifiers operating with a wick operate similar to cascade humidifiers as surface humidifiers. But the air does not come in close contact with the water because of the wick. It passes by the moistened wicks which absorb heated water from a storage tank. These humidifiers have the same drawbacks as the cascade humidifiers, but since they can be built smaller they can be arranged closer to the patient. The problems of condensation are thus less pronounced but the requirement for sufficient humidification of the respiratory air is more problematic.
Another humidifier employs hot steam injection into the inhaling air current. For the production of the hot steam, a heated plate is arranged in the humidifier in which an adjustable amount of water is evaporated. The generated steam flows into the inhaling air system and humidifies and heats the system. The humidifiers according to this system can be built very small. Condensation is therefore no problem but the adjustment of the amount of water for proper humidification is difficult. A respiratory volume which is too small may result in overheating while a volume which is too great may lead to inadequate humidification and too low temperatures.